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The Ear
Functions of the Ear
1. Hearing2. Balance
There are three parts to the Ear:
1.The Outer Ear
2.The Middle Ear
3.The Inner Ear
Anatomy of Ear
•Auditory canal•Tympanic membrane•Pinna•Ossicles•Oval window•Round window•Cochlea
•Organ of Corti•Semicircular canals•Utricle•Saccule•Otoliths•Auditory nerve•Outer/middle/inner ear
Ear Anatomy…
Anatomy of the Ear
Outer Ear Function: To gather sound waves,
causing the ear drum to vibrate. Made of skin and cartilage. The ear flap is called the pinna.
Outer EarPinna
Ear flap (cartilage) Funnels sound into auditory canal
Auditory Canal Leads into the head Lined with wax secreting cells
Tympanic Membrane (aka. Ear Drum) End of the auditory canal Separates outer ear from middle
ear
Mid
dle
Ear
The Eardrum is connected to the three smallest bones in the body:-Malleus (hammer)- Incus (anvil)- Stapes (stirrup)
Together these are known as the ossicles.
Mid
dle
Ear The bones are attached to each
other by ligaments that allow them to move back and forth & AMPLIFY the sound!
The last ossicle, the stirrup, is attached to the oval window.
Sound Intensity and Pitch
Sound intensity - depends on number of neurons and frequency of firing
Pitch (hi or low note) - each hair cell responds to only one frequency.
Ear Test
The eustachian tube is located just after the eardrum, in the middle ear.
The Eustachian tube connects to the throat and allows for pressure equalization on both sides of the tympanic membrane.
How do we equalize pressure?
Mid
dle
Ear
Size of tube compared to coin
Inner Ear
Function#1: Hearing. Converts sound vibrations from the ossicles into nerve impulses!!!
Function #2: Balance. The Cochlea is the organ that is
responsible for hearing (this is the place where neurons attach).
The Cochlea is coiled, like a snail shell.
It is divided into scala vestibule and scala tympani by the cochlear duct.
Cochlea – Cross Section
Inner Ear
The cochlear duct contains the Organ of Corti where sound receptors (four rows of hair cells) are found.
A fluid (called endolymph) surrounds the Organ of Corti.
The scala vestibuli and the scala tympani contain another fluid called perilymph.
The utricle, saccule, and semicircular canals are responsible for balance and body position
The Mechanics of Hearing
Longitudinal sound waves travel down the auditory canal.
Tympanic membrane vibrates. Ossicles (malleus, incus, & stapes)
move. Stapes is connected to the oval
window. When the stapes moves, it causes this window to bulge.
The oval window bulging causes the fluid in the outer two parts of the cochlea to move.
This puts pressure on the cochlear duct.
The Mechanics of Hearing
The pressure waves cause the basilar membrane to move which causes the hairs in the organ of Corti to bend against the tectorial membrane.
As the hairs bend, the small nerves that are connected to the base of the hairs are stimulated.
These nerve impulses are carried to the brain along the auditory nerve.
the temporal lobe of the cerebral cortex interprets the impulses as sound.
The Mechanics of Balance
The utricle, saccule, and semicircular canals are important structures for balance & are filled with fluid and contain sensory hairs.
The utricle & saccule contain small calcium carbonate particles called otoliths (ear stones).
Movement of the head ( along one plane – horizontal/vertical), causes the otoliths to move in response to gravity. These particles cause sensory hairs to bend, triggering impulses which alert the brain as to the position of the head.
The saccule contains sensory hairs as well
The Mechanics of Balance
The semicircular canals contain sensory hairs which are bent by movement in the fluid surrounding them. One canal detects bending forward and backward, another detects bending left or right, and a third detects a turning motion.
The brain then signals the appropriate muscles to maintain balance.
Semicircular Canals
Ear SafetySmall muscles in your ears help
protect your hearingWhen loud noises are around,
1. Muscles attached to the hammer (malleus) contract and restrict intense movements.
2. A second muscle contracts pulling the stirrup (stapes) away from the oval window limiting inner ear damage.
Not effective with sudden loud noises This response takes time. Sudden noise causes huge damage to
inner ear, specifically the hairs in the Organ of Corti
What structures are for hearing?
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